Question

what is the difference between a pure substances and non-pure substance?

Answer 1

A pure substance contains only one kind of matter with a fixed, uniform composition and characteristic properties. A non-pure substance (more commonly called a mixture or impure substance) contains two or more different substances physically combined, with variable composition and properties that depend on the amounts of the components.

Key differences
- Composition:
- Pure substance: single chemical species (an element or a compound).
- Mixture: two or more different substances mixed together.
- Uniformity:
- Pure: identical properties and composition throughout.
- Mixture: may be uniform (homogeneous) or non-uniform (heterogeneous).
- Physical properties:
- Pure: sharp/fixed melting and boiling points.
- Mixture: melting/boiling over a range or altered values.
- Separation:
- Pure compound: requires chemical reactions to separate into elements.
- Mixture: components can be separated by physical methods (filtration, distillation, chromatography, etc.).
- Examples:
- Pure: distilled water (H2O), elemental oxygen (O2), crystalline sodium chloride (NaCl).
- Mixture: air (homogeneous mixture of gases), seawater, soil, salad (heterogeneous), brass (alloy).

Tests for purity often include measuring melting/boiling points, chromatography, and spectroscopy.